In an indicating instrument for a vehicle, various methods has been proposed to provide an enhanced appearance. For example, it is proposed to provide a display board with a metallic, lustrous surface, thereby to improve a quality appearance. In this case, however, if an external light, such as, a sunlight, is reflected on the display board while the vehicle is running, it is likely to blind a driver and reduce visibility.
In an indicating instrument disclosed in JP-A-2003-156369 (U.S. Pat. No. 6,886,970 B2), a light transmissivity of a light modulation film is controlled based on illumination conditions of a display board so as to maintain the visibility. Namely, when the display board is relatively bright, the light transmissivity of the light modulation film is controlled to a relatively low level. On the other hand, when the display board is relatively dark, the light transmissivity of the light modulation film is controlled to a relatively high level.
Incidentally, while the vehicle is running, the quantity of external light incident on the display board occasionally momentarily changes depending on driving circumstances. The driver is unlikely to sense such an instant change of the incident light because of visual characteristic. In this case, if the light transmissivity of the light modulation film is linearly changed with the instant change of the incident light, it is likely to cause flicker and deteriorate visibility of the display board.